Flat panel displays have rapidly become ubiquitous in various markets, and are now commonly utilized in a variety of appliances, televisions, computers, cellular phones, and other electronic devices. One example of a commonly used flat panel display is the thin film transistor (TFT) liquid crystal display (LCD), or TFT-LCD. A typical TFT-LCD contains an array of TFTs each controlling the emission of light from a pixel or sub-pixel of an LCD. FIG. 1 depicts an idealized cross-section of a conventional TFT 100 as might be found in a TFT-LCD. As shown, the TFT 100 includes a gate electrode 105 formed on a glass substrate 110. A gate insulator 115 electrically insulates the gate electrode 105 from overlying conductive structures. An active layer 120, typically composed of amorphous silicon, conducts charge between a source electrode 125 and a drain electrode 130, under the electrical control of gate electrode 105, and the conducted charge controls the operation of the pixel or sub-pixel connected thereto (not shown). A source/drain insulator 132 electrically isolates the source electrode 125 from the drain electrode 130 and protectively seals the TFT 100. As shown, the gate electrode 105, source electrode 125, and drain electrode 130 each typically includes a barrier metal layer 135 and a metal conductor layer 140 thereover. The barrier 135 provides good adhesion between the conductor 140 and the underlying glass and/or silicon and reduces or prevents diffusion therebetween.
Over time, LCD panel sizes have increased and TFT-based pixel sizes have decreased, placing increasingly high demands on the conductors within the TFT-LCD structure. In order to decrease the resistance in the conductors and thereby increase electrical signal propagation speeds in the TFT-LCD, manufacturers are now utilizing low-resistivity metals such as copper (Cu) for the conductors 140 within the display. Metals such as molybdenum (Mo), titanium (Ti), or molybdenum-titanium alloys (Mo—Ti) have been utilized for barriers 135 underlying Cu conductors 140. However, particularly as feature sizes continue to shrink, the processing of such metals presents difficulties during the fabrication of the TFT-LCD. For example, as shown in FIG. 2, during the etching of electrodes such as gate electrodes 105 with conventional wet etch chemistries, either an etch residue 200 (of one or both electrode materials) or etch discontinuities 210, e.g., stepped or nonlinear profiles (caused by non-uniform etch rates of the two different electrode materials), may result.
In view of the foregoing, there is a need for improved etch chemistries usable during the processing of metal bi-layers for electronic devices such as TFT-LCDs and that enable such etching to be performed with only minimal (if any) non-uniformity in etch rate and without producing deleterious etch residue.